The largest deposits of selenium-rich soil ever found in China have been discovered in the country's southernmost province of Hainan after seven years of exploration, a local geologist said Tuesday.

Xi Xiaohuan, a senior engineer with the China Geological Survey, noted that selenium-rich soil covers a total area of 9,545 square kilometers, or more than 28 percent of the total area of the island province.

Xi said the selenium-rich soil is clean enough to allow Hainan to develop environmentally friendly selenium-enriched farm produce.

According to Li Haizhong, head of the Hainan Geological Survey, Hainan has already demarcated areas that will be suitable for growing selenium-rich rice fruits and betel nuts.

Selenium is a chemical element and an important micronutrient. Selenium can boost the immune system, slow down the aging process and reduce the effects of cardiovascular diseases.

Hainan is an important agricultural base for China, producing a variety of tropical fruits and vegetables.